Wrapping the exhaust keeps the heat in the pipe. Increased temperatures in
the pipe promotes greater exhaust gas velocity. Keeping the heat in the pipe
is also better than having it in the engine compartment. The heat in the
pipe also promotes fatigue of the downpipe. Keeping the downpipe that hot
all the time can lead to cracking. Are there performance gains? Probably
noticeable on the track, I doubt we would notice it on the street, but hey,
every little bit helps. Be aware of the chance that your downpipe may crack
from all that heat you're keeping in there.
Michael
92 S4